With the development of the modern society, the diversification of people's life and popularization of information communication make the broadband internet access become a part in people's life. This makes the broadband access technology to develop towards a direction of becoming broader and faster. The original Gigabit Passive Optical Network (GPON) can less satisfy some people's increasing requirements, and then it is a trend to upgrade the GPON to be 10 Gigabit Passive Optical Network (XGPON1) in the near future. It will be an inevitable reality for a quite long time that both GPON and XGPON1 coexist in one Optical Distribution Network (ODN) since not every user demands upgrading immediately.
In addition, after a large number of the Passive Optical Networks are arranged and deployed, the operator will consider the operation and maintenance of the networks, especially the detection of an optical fiber line and fault location. In order to reduce the maintenance cost, the operator would like to detect the whole Passive Optical Network with an Optical Time Domain Reflectometer (OTDR) in a Central Office (CO) so as to facilitate the detection and conduct a real-time detection without interrupting the service.
Therefore, a wavelength division multiplexing filter that can satisfy coexistent requirements of the GPON and the XGPON1 and has an OTDR interface is demanded.